This invention relates generally to security systems that provide visual records of trespassers that approach entryways to buildings. More specifically, the invention relates to simple low-cost security systems that are suitable for protecting homes and small offices.
Security systems presently exist which detect persons, animals, and other objects approaching entryways to buildings and then turn on a television camera as a means of obtaining an electronic record of the event. The television camera signal is either transmitted over a video-bandwidth communication link to a building occupant or recorded on magnetic tape at the camera location. In the latter case, an alerting signal is transmitted over an audio-bandwidth communication link to the building occupant who investigates the occurrence by visiting the camera site and playing back the tape.
The cost and complexity of such systems generally make them unsuitable for use in homes and small offices. In addition, the lack of a screening mechanism that would cause the security system to ignore entries into the building by authorized persons is a serious defect in buildings where a large amount of such traffic is to be expected.